Resolve remote address placeholder for Nethernet connections

Use unique 0.x.x.x placeholder addresses instead of 0.0.0.0 for each
connection to prevent per-IP collisions in downstream software.

Real IP resolution from ICE candidate pair stats is commented out as
reference - it works but delays channel activation, causing pipeline
timing issues. Requires a synchronous getter in the webrtc-java JNI
layer to avoid the delay.